In recent years, optical glasses excellent in light transmittance have been incorporated and used in various devices. Specifically, these optical glasses are employed for core parts of multi-component glass fibers used as light guides, image guides or industrial endoscopes, or glass lenses for i-line used in semiconductor exposure devices (see catalogues for i-line, published by Ohara Inc.).
It is necessary for the multi-component glass fibers that a material with a higher refractive index (nd) is used for core parts in order to increase a light transmission intensity and a material with a lower refractive index is used for clad portions in order to raise a numerical aperture. Furthermore, it is important that transmittance is high over an entire visible range since optical fibers are often used for longer transmission routes and lower transmittance results in a larger transmission loss.
Patent Document 1 discloses an optical glass, used for core parts of multi-component glass fibers, which contains 34% to 49% of SiO2+B2O3, 6% to 13% of Na2O+K2O, 10% to 30% of BaO, 6% to 16% of ZnO, 1% to 15% of La2O3+ZrO2, and 0% to 20% of PbO on the basis of mass percent.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2006-117504